Constraints on modified gravity from the BOSS galaxy survey

Abstract

We develop a pipeline to set new constraints on scale-independent modified gravity, from the galaxy power spectrum in redshift space of BOSS DR12. The latter is modelled using the effective field theory of large-scale structure up to 1-loop order in perturbation theory. We test our pipeline on synthetic and simulated data, to assess systematic biases on the inferred cosmological parameters due to marginalization and theoretical errors, and we apply it to the normal branch of the DGP model with a ΛCDM background. When applied to synthetic data and cosmological simulations, we observe biased posteriors due to the strong degeneracy between the nDGP parameter Ωrc and the primordial amplitude of fluctuations As . Fixing the latter to the Planck central value, we obtain a posterior distribution with Ωrc ≲ 0.65 at 95% C.L., under the assumption of a flat prior on log10 Ωrc. This upper bound, however, depends strongly on the prior on Ωrc. To alleviate this effect, we provide an upper bound based on the Bayes factor between the nDGP model and ΛCDM model, which gives Ωrc ≲ 0.2 at 95% C.L..

The effective field theory of large-scale structure and multi-tracer

“…This approach builds upon the effective field theory of LSS (EFTofLSS) [8][9][10][11][12][13] and the large-scale bias expansion of matter tracers [14,15]. It has achieved remarkable results when applied to BOSS data [16][17][18][19][20][21][22] and when probing new physics [23][24][25][26][27][28][29][30]. One of its downsides is that it requires a few free parameters (counter-terms, bias, and stochastic coefficients) to be fitted in data, although those parameters have a clear physical motivation and guarantee the correct parametrization of structure formation on the mildly non-linear regime.…”

Improving precision and accuracy in cosmology with model-independent spectrum and bispectrum

“…In ΛCDM they are usually approximated by their EdS values [44], listed in (A.10), which turns out to work at the subpercent level on the scales of interest [45,46]. In theories beyond ΛCDM, on the other hand, the effect can be larger, expecially in models featuring nonlinear 'screening' of extra degrees of freedom [19,47].…”

“…Cosmic chronometers have many possible source of systematics related to astrophysical model assumptions, but these are expected to be unrelated to the background cosmology. The redshift drift is also an alternative, but lies JCAP01(2024)001 [79], which was constrained recently using the BOSS data [19] and an evolving dark energy with equation of state w(z) = w 0 + w a z/(1 + z). Correlations among the error bars are small.…”

“…Figure 7 shows the results for the marginalized 1-σ errorbars for the growth function f (z) and the bootstrap function d (2) γ (z). In these plots we also show, for comparison, some models beyond ΛCDM that are still phenomenologically viable: the normal branch of the DGP model [79], which was constrained against the BOSS data recently [19], and an evolving dark energy with equation of state w(z) = w 0 + w a z/(1 + z). Our analysis shows impressive results for the growth function: the P + B analysis has the full potential to distinguish among different cosmological models.…”

“…EFT-based models for the power spectrum at one loop have been recently used for the analysis of the BOSS dataset [6], giving constraints on cosmological parameters that are competitive with CMB based observations [7][8][9][10][11]. The results of these and following data analysis (constraints on neutrino masses [12,13], H 0 tension [14,15], beyond-ΛCDM model [16][17][18][19], redshift space distortions [20,21]) represent a great step forward in the study of LSS within the EFTofLSS framework. Moreover, in the BOSS collaboration the bispectrum has been measured and analyses have been performed [22][23][24], while the first detection of the BAO features in the bispectrum has been claimed in [25].…”